Ultrasonic Characterization of Elastic Anisotropy in Composites: Case Study of CFRP

Combined measurements of bulk and plate wave velocities are used to infer the complete matrix of elastic constants for orthotropic CFRP laminates. A direct estimate of Young's moduli in principal axes of the composite is deduced from the low-frequency values of the s(0)-wave velocities in these directions. The non-contact ultrasonic evaluation of the in-plane anisotropy of Young's modulus in CFRP is implemented by air-coupled measurements of the a(0)-wave dispersion extrapolated to a static case. A strong variation of elastic anisotropy as a function of frequency is measured for both s(0)- and a(0)-waves. A simple phenomenology presented enables a rapid quantification of frequency variation of plate wave anisotropy in composites. The relation between elastic wave anisotropies and inherent material elasticity is discussed for bulk, surface, and plate waves.